Process of treating crude cyanide



Patented May 1926.

UNITED ATES PATENT OFFICE.

norm-n E. enovnn, m, AND rnomas neuron noenns, or WILMINGTON, DELAWARE,

assrenoas 'ro E41. no rom nn nnmoons a commmz, or wrnmna ron, DELA- warm, A conronarrron or DELAWARE. a

PROCESS TREATING CRUDE CYANIDE.

, No Drawing.

a This" invention relates to production 'of alkali-metal cyanides from crude cyanide containing a soluble alkaline e'arth metal salt.

Theimain-object of our intention is" provide anew and improved method for, 17

obtaining substantially pure solutions of so-,

dium or other stable metal cyanide ,from crude cyanides containing soluble calcium, or its equivalent. v

The crude cyanide to'be used as raw material may be, for example, a product, ob-

tainable in'the open market, which contains as soluble constituents, --25% cyanogen, 11v-20% soluble calcium, I l-17 sodium,- 22-25% chlorine; withabout 15% CaO and 5-10% of various inert impurities.v ,This

water. The presence of calcium-in cyanide solutions causes deco osition, Presence of the products of deco V position, azulnnc acid,

et c., induces and ha stens further ,decompo-a sition.

crudecyani'de and tthe same time free the solution'of calcium, substituting sodium or other alkali-metal therefor, relatively stable solution of an alkali-metal cyanide is obtained, which, except for thepresence of sodium chloride, is of high degree of'ipurity.

This solution inaybe used for Various proc-fl ance, gold extraction, gen

esScs as, 1 01 in t cration of llQlN, and {puny chemicalsyntheses. l I f a a If, in convcl'itiug the crude cyanide into sodium cyanide, the leached-with whiter, the insoluble jnfitter' filtered oil, and calciuni precipitated from the filtrate by addition f, for instance, so-X ll result. a serious; loss of cyanidel 'tlue to le fact that a con dium carbonatdilthere p1 jbined calcium residerable amount of c I ibstantial period mains in solution for T before precipitation is more, the solution fro: 'has been precipitatediigitends to'vhbecome thick, due to the formEtion and deposition of a brown decompositi n product; azulrnic acid, which renders filration uni-ch more acy d I We have found: that the amount of Pre Wefhave idiscoverdthat' if we leach the cipltatingagentprdinarily depends on the gtiiude material be ected. ,Furthervhich the calcium,

" to that; correspon Application fi1ed re-wh m, 1921. Serial No 451,768.

difiicult. The mere addition of crude cyanide to the leachin liquor in large quantity causes somuch t icl rness in the solution thatlm has not been practicable to obtain by-this rocedure solutions stronger than a-N N e have found it possible to avoid the above difficulties by-accomplishing both the dissolved. Some diifi'culty may be experiencedthrough precipitation of the calcium salt in a gelatinouso'r colloidal condition if the reaction is allowed to. occur between stron 1utipns ofiq'alcium ion and the calciumprecipitating 5 ion. We have obfvi atedthis" by adding the two materials,"

the crude cyanide, and the precipitating agent,-=to'the leach liquor in small batches lntheproper ratio over a longer period of time; The addition of a ba'clr of precipitating agent should prec'ed "jthat of the cyanide content oh cyanide, and

be'calculated 'from thatl t s well as from the soluble calcium contentfill A sufficient amount of the reci itating i ent may be added to cause in tran formatioh of the calcium hydroxide resen also int a less soluble salt, as for instan e,.'into\ c, lcium carlbonate (when s diu arbonate is the precipitating age t). 11's" howevler, is not necessary, as e solub lity' of calcium b droxide s diminished in the presence of the othelfli 'salts, (NaCN NaCl and NaOH formed-byes. ticizatio of excess Na CO bythe Ga( H 2 in sludge), and the calciui sulting isjnQtsuifidient 0 causeerious de-. compositionfi 5 We'have fourifi it co yenient to prepare 20-25% sodium ,;."'cyanide solutions for use, but the general precess embraces the preparation ofsolutiqii fs' of any concentration 'up a n to the solubilit of sodium-cyanideng'yvater saturated wit sodium chloridey the degree of concentration he crude cyanide concen ration reof the solution being controlled by the ratio of water to crude cyanide employed. The precipitating agent may be the lkali-metal salt of any acid whose calcium salt is sub stantially insoluble, such as sodium or pot-assium sulphate, but We have found it most convenient to use sodium carbonate for this purpose.

()ur preferred procedure may be i1lustratcd by the following example: 'lwo parts by weight of water are used to leach one part by weight of the crude cyanide. A quantity of sodium carbonate chemically equivalent to the soluble calcium in the crude cyanide, with about five percent excess, is weighed out. These two constituents, the crude cyanide and the sodium car-- bonate, are either mixed thoroughly and added to the water,.or else added in equivalent batches. in either case slowly and over a period ottime. In the latter case the addition of a batch 01 sodium carbonate precedes that oi the crude cyanide. The calcium immediately upon going into solution, ell her as the chloride or cyanide, is precipitated according to the reactions:

In both cases the whole amount of material is added in 12 or 15 batches over a period of 1-2 hours. -Thc mixture is meanwhile kept in a state ol' rapid agitation, in order to ensure the complete disintegration of the llakcs of rude cyanide. and the solution of itscoutainml cyanide.' The resulting slurry, a l'ter complete solution is etlected, is filtered and the solution of sodium cyanide 0btaiucd. "he sludge may'be washed free of cyanide in order to increase the recovery.

For the production of stronger solutions, either the filtered solution, obtained as described, or the wash liquor, may be used to leach an additional quantity of the crude cyanide, using the same procedure with water. I urthermore, it the sodium hydroxide concentration of the purified solution is too great. due to involuntary Zldtll? ion of too great an excess of sodium carionatc', resulting in the reaction this tree-alkalinity may be reduced to the desired extent by addition of corresponding quantities of the crude "cyanide before or after the sludge is filtered oli'.

We have studied the decomposition of solutions ol sodium cyanide, bothin the pres once 01" a considerable proportion of dissolved calcium. and in the presence of a very small proportion of calcium corrcspoiuling to the solubility of Ca.(()ll). which is alnayspresent in the sludge due to the Cat) content otthe criulecyani-'-le. \Ve have thus proven the. serious decomposability oi solutions of calcium cyanide, as compared with the re atively great stability of solutions froniwhich thecalcium has been precipitated. Two slurrics and a clear solution were investigated, the. first slurry (I) being obtained by leaching crude cyanide with a 10% solution of sodium cyanide, without addition of sodium. carbonate, hence containing much calcium in solution, as well as in the sludge; the second slurry being obtained by leaching crude cyanide with a ltlfll solution of sodium cyanide, with addition ol sodium carbonate in amount slightly in excess of that equivalent to the soluble calcium, thus leaving calcium in the sludge, and in the solution also, but only to the extent of the solubility of Ca(()H) and clear solutions (3) being obtained by leaching and filtering as described in our preferred procedure, and thus saturated with Ca(()1l). The percentages of cyanide lost by decomposition are given in the following tables:

Percentage NaC'N loss by decomposition.

1 l 1hr. t Hus. lday.

Temperature 60 (7.: l (1) 16% NnCN solution (4% iPer can! Pe cm! Per cenl Pcr ceal olids l o. 10 7. 2 3

ealcium)+s 19 U l (2) %solution+solu1s 0.85 1 57 5.5 i 221.1

' s utlonunc 0.06 1 G2 3.65 I 14.8

(3) 11.n solution... 5 U U 3 1 54.5 15.21

'lcnzperature 30 (7.:

(1) 16% NaCN solution (4% calcium)+solids r 7,1 7.15

(2) 20% solution+sol ds l U. 415 1. 66 1. 75 ll. 75

t) 20% solution 0.0! 0.35 1 0G I 4.2

Our decomposition experiments also containing a soluble alkaline earth metal saltwliieh comprises dissolving said salt and then immediately efi'ecting precipitation of the alkaline earth metal.

2. The process of treating a crude'cyanicle containing a soluble alkaline earth metal salt which comprises subjecting said crude cyanide to the action of a solvent for said salt, said solvent containing a substance capable of reacting with dissolved portions of said salt to term an insoluble alkaline earth metal compound.

3. The process of treating a crude calcium cyanide which comprises subjecting said cyanide to the action of a solvent therefor and cli'ecting precipitation of calcium ions in lweek. I

calcium salt in Water containing a. substance capable of reacting with the calcium in solution to form an insoluble calcium compound.

5. Theprocessof treating a crude cyanide.

containing a soluble alkaline earth metal salt which con'iprises dissolving said salt and then immediately effecting precipitation of the alkaline earth metal while maintaining the solution at a temperature below 40 C.

6. The process of producing an alkalimetal cyanide from a crude cyanide containing an alkaline earth metal salt which comprises treating said crude cyanide with a Water solution of an alkali-metal carbonate.

7. The process of cyanide from crude calcium cyanide which comprises treating said crude cyanide with a Water solution of sodium carbonate to cause precipitation of the calcium as soon as it becomes dissolved.

producing sodium 7 8. The process of producing sodium cyan ids-from crude calcium cyanide which coinprises treating said crude cyanide with water in the presence of sodium carbonate to form calcium carbonate and filtering off the latter along with other insoluhlematter which may have been present in the crude cyanide.

9. A process as defined in claim 2 in which the ratio of solvent to soluble alkaline earth metal salt is such that the alkaline earth metal can be precipitated from the resulting solution of said salt in a form which makes it readily removable by filtration.

10. A process as defined in claim 7 in which the proportion of calcium undergoing precipitation at any one time is small compared to the proportion of Water present.

11. A process as defined in claim 8, in which the proportion of calcium undergoing precipitation at any one time is small compared. to the'proportion of water present.

i In testimony whereof we afiin our signatures.

R LEE E. GLOVER, JR.

EJEI'XS HUNTON ROGERS. 

